Iraq says it will take steps to bring an American private security firm to justice after a U.S. judge dropped charges against five security guards accused of killing Iraqi civilians in 2007.

A spokesman said Friday the Iraqi government will ask the U.S. to appeal the decision. The spokesman said it is "regrettable," because an Iraqi investigation found that the men committed a crime.

The guards worked for Blackwater Worldwide, now known as Xe Services.

U.S. prosecutors charged them with opening fire on unarmed civilians in a crowded Baghdad intersection in September 2007, killing 17 people.

A U.S. federal judge dismissed the charges Thursday, because the U.S. government had violated the guards' constitutional rights.

The company's chairman and CEO issued a statement supporting the court's decision. But the top U.S. commander in Iraq, General Ray Odierno, says it could lead to a backlash against other security firms working in Iraq.

U.S. District Judge Ricardo Urbina said prosecutors improperly used statements from the defendants that had been given under a promise of immunity. Urbina said the government's explanations were "contradictory, unbelievable, and lacking in credibility."

A sixth guard has already pleaded guilty to manslaughter charges.

A U.S. Department of Justice spokesman says prosecutors were considering options in the case.

Following the shooting, Blackwater Worldwide lost its license to operate in Iraq, along with many of its lucrative contracts with the U.S. State Department.